1. Field of the Invention
The present invention generally relates to a common rail such as a high pressure fuel manifold in a diesel engine or a block rail.
2. Description of the Prior Arts
Conventionally, various kinds of common rails of this type having various kinds of shapes have been suggested. For example, as shown in FIGS. 8 and 9, there has been known a so-called boss type common rail which is structured such that a branch hole communicating with a communication passage 11-1 of a main pipe rail 11 and having a pressure receiving seat surface 11-4 open to an outer direction is pierced in a plurality of boss portions 11-3 disposed in an axial peripheral wall portion of the main pipe rail 11 having an outer peripheral surface formed in a complete round shape at an interval, a pressing seat surface 12-3 formed by a connection head portion 12-2 of a branch pipe 12 end is brought into contact and engaged with the pressure receiving seat surface 11-4 of the main pipe rail 11 end, and a fastening outside screw nut 13' or a ball head lock nut 13" previously assembled in the branch pipe end is meshed with an inside screw or an outside screw disposed on an inner peripheral surface or an outer peripheral surface of the boss portion 11-3, so that the common rail is fastened and connected together with pressing under a neck portion of the connection head portion 12-2. In FIGS. 8 and 9, reference numeral 12-1 denotes a flow passage of the branch pipe 12, reference numeral 14' denotes a fastening sleeve washer and reference numeral 14", denotes a washer.
Further, as shown in FIG. 10, there has been known a so-called sleeve nipple type common rail which is structured such that a branch hole 11-4 portion communicating with an inner communication passage 11-1 disposed in a peripheral wall portion of a main pipe rail 11 end constituted by a circular pipe is made a pressure receiving seat surface 11-4 open to an outer direction, a cylindrical sleeve nipple 15 is mounted to an outer peripheral wall of the main pipe rail 11 adjacent to the pressure receiving seat surface by welding, and a pressing seat surface 12-3 constituted by a connection head portion 12-2 of a branch pipe 12 end is brought into contact and engaged with the pressure receiving seat surface 11-4 of the main pipe rail 11, thereby fastening and connecting together with pressing under the connection head portion 12-2 neck by means of an engagement between the inner screw disposed on the inner peripheral surface of the sleeve nipple 15 and the fastening nut 13' previously assembled in the branch pipe end.
Still further, as shown in FIG. 11, there has been known a so-called joint metal fitting type common rail which is structured such that a branch hole 11-2 portion communicating with an inner communication passage 11-1 disposed in a peripheral wall portion of a main pipe rail 11 end constituted by a circular pipe is made a pressure receiving seat surface 11-4 open to an outer direction, and pressing seat surface 12-3 constituted by a connection head portion 12-2 of a branch pipe 12 having a tapering conical shape and enlarged a diameter thereof by buckling is brought into contact and engaged with an end portion by using a ring-like joint metal fitting 16 surrounding an outer peripheral portion of the main pipe rail 11 adjacent to the pressure receiving seat surface, thereby fastening and connecting to a screw wall 16-1 portion projecting to the joint metal fitting 16 together with pressing under the connection head portion 12-2 neck by means of an engagement between a fastening sleeve washer 14' and a fastening nut 13' previously assembled in the branch pipe end.
However, in the case of the boss type common rail which is structured such that the branch hole 11-2 is provided in the boss portion 11-3 integrally formed in the main pipe rail 11 having the outer peripheral surface of a complete round shape, as shown in FIGS. 8 and 9, the sleeve nipple type common rail which is structured such that the cylindrical sleeve nipple 15 is directly mounted to the main pipe rail 11 by welding and the nut 13' meshed with the sleeve nipple 15 is fastened and connected, as shown in FIG. 10, and the joint metal fitting type common rail which is structured such that the ring-like joint metal fitting 16 is outwardly fitted to the main pipe rail 11 and the nut 13' meshed with the ring-like joint metal fitting 16 is fastened and connected, as shown in FIG. 11, a great stress is generated in an inner peripheral edge portion P of a lower end of the branch hole 11-2 due to an axial force applied to the pressure receiving seat surface 11-4 together with the internal pressure of the main pipe rail 11 and the pressing of the connection head portion 12-2 in the branch pipe 12, so that a crack is easily generated with starting from the lower end inner peripheral edge portion P and there is a possibility of inviting a leakage.